The penetration of ciprofloxacin in pancreatic juice was investigated in 5 patients with pancreatic fistula. The drug was administered as a single oral dose of 500 mg after which serial samples of pancreatic juice and serum were collected for ciprofloxacin assay. The following pharmacokinetic parameters (mean +/- SD) were estimated from the serum level versus time curves: clearance 11.51 +/- 2.85 (ml/min/kg); Vd area 3.08 +/- 1.20 ml/kg; terminal half-life 3.10 +/- 0.92 h; mean residence time 5.64 +/- 1.40 h. Ciprofloxacin serum levels declined rapidly after the third hour, whereas concentrations in pancreatic juice remained elevated (above 1 mg/1) for nearly 12 h. The pancreatic juice/serum ciprofloxacin concentration ratio increased gradually fom 0.63 +/- 0.45 after 0.5 h to 6.18 +/- 4.59 after 12 h (mean +/- SD). Our data indicate that while the drug elimination half-life from the serum is short, the time-course of ciprofloxacin levels in the pancreatic juice conforms to a much slower disappearance rate. In particular, the ciprofloxacin levels achieved in pancreatic juice are constantly greater than the MICs of the bacteria generally responsible for pancreatic infections.